In this study, a 1,4,7,10-tetraazacyclododecane (cyclen)-based side-chain homopolymer was developed for the first time; this polymer can self-assembly with plasmid DNA to form polyelectrolyte complexes (polyplex), which can protect DNA from enzymatic degradation. Moreover, the polyplex can disassembly and release free DNA when NaCl solution is added to this system. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used for imaging of the surface structure of the polyplex, and results indicated that the polyplex structures respond to the polymer concentration. Circular dichroism (CD) spectrum suggested that the DNA configuration in the polyplex was retained.